This invention relates generally to cold cathode-type vacuum gauges, and more specifically relates to a vacuum gauging system especially suited for large-scale use in a facility having a plurality of separate vacuum system which do not require continuous pressure monitoring.
This invention was made during the course of, or under, a contract with the Energy Research and Development Administration.
A cold cathode vacuum gauge, sometimes called a Penning or Philips gauge, is used to measure vacuum pressures by measuring the current due to positive ions produced by electrons with gas molecules between a cathode and an anode electrode in the vacuum medium being measured. A magnetic field is applied between the cathode and anode to increase the electron path length between the two electrodes so that the probability of collision of the electrons with the sparse population of gas molecules is increased to produce positive ions. A high voltage, usually between 2 and 4 KV, is applied between the electrodes. An ammeter calibrated in pressure units reads the current between the cathode and anode as a measure of the pressure.
In a large gas centrifuge plant, many thousands of individual centrifuges are to be operated continuously. Plans now call for installing a vacuum gauge preferably of the cold cathode type in the vacuum casing of each centrifuge where it will be used for several purposes. For example, the vacuum gauge is needed to monitor the casing pressure (region of 10xe2x88x925 to 10xe2x88x923 torr) during startup of the centrifuge. If the pressure is not as low as it should be, the centrifuge will not accelerate properly, and as a consequence costly downtime will be increased.
Another reason for maintaining vacuum gauging capabilities in each centrifuge casing is in the diagnostic measurement of an over-pressure condition in an operating centrifuge. In this case, some other diagnostic means, perhaps a deceleration circuit, may be used to indicate a centrifuge is failing because of loss of rotor speed. If the cause is from some means other than pressure, immediate action may not be necessary. But if the casing pressure is building up, immediate action must be taken. A pressure measurement made at such time reveals that the loss in speed is due to rising pressure, verifying the need for isolation and deceleration of the rotor of the centrifuge.
In this and other diagnostic applications, the vacuum gauge is not operated continuously. In fact, it is to be turned xe2x80x9conxe2x80x9d only during these infrequent pressure measurements. The reason for such a mode of operation is that the UF6 environment in the centrifuge and the high voltage on the cathode unit of the gauge itself tends to degrade the instrument over a period of time. In a large centrifuge plant then a vacuum gauge is required in the startup of every centrifuge, and a capability to make a pressure reading on any centrifuge at any time thereafter must be maintained. In the quantities needed, however, the price of an individual cold cathode vacuum gauge for each vacuum casing in a gas centrifuge cascade is quite expensive. Thus, there is a need for a vacuum gauging system which will meet the objectives and requirements of a gas centrifuge cascade and yet minimize the costs for adequate pressure monitoring.,
In view of the above need, it is an object of this invention to provide a vacuum gauging system of the cold cathode type for selectively measuring the pressure of a plurality of separate vacuum systems which is considerably less expensive than providing a separate vacuum gauge for each vacuum system.
Another object of this invention is to provide a vacuum gauging system as set forth in the above object in which a gauge tube assembly including the anode and cathode electrode structure of the gauge is mounted with each vacuum system casing and a portable means is provided to be selectively connected to the gauge tube to apply a magnetic field in the area between the anode and cathode electrodes and provide a pressure readout indicated by the magnitude of current flow between the cathode and anode electrodes when a high voltage is applied therebetween.
Further, it is an object of this invention to provide a vacuum gauging system as set forth in the above objects which may be used with the vacuum casings of a gas centrifuge cascade.